When a conventional inner cable having little tightening percentage and large pre-forming percentage, an inner cable with loose strand is used at a site such as a non rotating guiding device where the inner cable is bent while sliding, shape is easily lost by the tightening percentage and pre-forming percentage and as a result, an element wire is subjected to local bending which is caused by pressuring the element wire on an element wire lay underneath by the secondary bending and external pressure; therefore there has been a problem that the durability of bending fatigue is low.
In an invention described in Japanese Patent Publication No. 2669754, there is proposed an inner cable for operation (hereinafter, referred merely as an inner cable) with a stranded construction which is constituted by stranding a core strand stranding a plurality of element wires with a plurality of side strands in which a plurality of element wires are stranded around the core strand, wherein the tightening percentage which is represented by the percentage of a value which is obtained by dividing a value obtained by subtracting a measured outer diameter being the diameter of the circumscribed circle of the inner cable for operation from a calculated outer diameter being the total sum of the inner cable for operation to a diameter direction of the respective outer diameters of the plurality of element wires, by the measured outer diameter is 4 to 11% and the pre-forming percentage of the side strand which is represented by the percentage of a value which is obtained by dividing the undulating diameter of the side strands when the inner cable is sleeved, by the measured outer diameter of the inner cable is 65 to 90%.
The inner cable described in Japanese Patent Publication No. 2669754 is hardly stranded by enlarging the tightening percentage than a conventional inner cable, deformation can be prevented and as a result, the secondary bending of element wires hardly occurs. Since force going to shrink to the central direction of the inner cable is applied to the side strand of the stranded inner cable, deformation can be prevented, effect that the secondary bending of element wires occurs hardly is obtained and the durability of bending fatigue at a sliding portion is improved.
FIG. 1 shows one example of the inner cable described in Japanese Patent Publication No. 2669754. The inner cable 1 shown in FIG. 1 is a so-called construction of 19+8×7. Wherein 19+8×7 is that one core strand 2 is composed by stranding 6 of the first side element wires 4 around one core element wire 3 and stranding 12 of the second side element wires 5 therearound, a side strand 6 is composed by stranding 6 of side element wires 8 around one core element wire 7, and 8 of the side strands 6 are stranded around the core strand 2 to prepare the inner cable 1. The core strand is a so-called cross lay construction and the first element wire is brought in a point contact with the second element wire.
Further, the tightening percentage of the present inner cable 1 is a range of 4 to 11% and the pre-forming percentage is a range of 65 to 90%.
The reason why the tightening percentage is a range of 4 to 11% is that when the tightening percentage exceeds 11%, element wires are hardly stranded and there are problems that wires are broken by excessive tightening or the surface of element wires is damaged in production. On the other hand, when the tightening percentage is lessened than 4%, durability subject to bending while sliding is inadequate, as will become clear from the from illustration by following Examples.
On the other hand, it is according to the following reason that the pre-forming percentage is set at a range of 65 to 90%. Namely, when the pre-forming percentage exceeds 90%, force going to shrink to the central direction of the inner cable is not applied to the side strand so much and secondary bending easily occurs when an inner cable similar to a non-rotating guiding device is used at a site where it is bent while sliding. Further, as will become clear from the illustrations of Examples and Comparative Examples described later, durability is lowered. On the other hand, the side strand is entangled at breaking in case of an inner cable having a pre-forming percentage of 65% or less, therefore it cannot be used.
The inner cable 11 as shown in FIG. 2 is another example of the inner cable of the invention described in Japanese Patent Publication No. 2669754. The inner cable 11 is those in which the core strand 12 is stranded in parallel lay strand (also called as line contact strand). The parallel lay strand is a strand type in which element wires with different outer diameters are combined and the strand pitch and strand direction of respective lays are the same. Since outer lay element wires are fitted in the groove portions between inner lay element wires, respective element wires are not crossed and essentially in line contact. As a result, the tightening of strand is good and shape loss hardly occurs. Further, it shows superior characteristics that the internal friction (friction by mutual element wires) of a strand is little and fatigue by the secondary bending is not generated.
The inner cable 11 of FIG. 2 has a W (19)+8×7 construction using the core strand 12 having a Warrington type construction within a parallel strand+8×7 construction. The Warrington type is that difference between the maximum diameter of element wires and the minimum diameter of element wires is the least and suitable for a strand with a narrow diameter in 19 of parallel lay stands.
Specifically, 6 of the first side element wires 14 with a slightly narrower diameter than the core element wire 13 are provided around one core element wire 13, 6 of the third side element wires 15 having the same diameter as the core element wire 13 are provided between the mutual first side element wires 14, 6 of the second side element wires 16 with a further narrower diameter than the first side element wires 14 are provided on an upper lay along the first side element wires 14, and these side element wires 14, 15 and 16 are simultaneously stranded at the same pitch and to the same direction to form the core strand 12. It should be noted that the diameters of the respective element wires of the core strand are not limited to the above-description. After all, when respective element wires are stranded at the same pitch and to the same direction, the diameter of element wires may be suitably selected so that respective element wires are mutually brought in line contact.
Further, 8 of the side strands 17 are strands in which 6 of side element wires 19 are stranded around the core element wire 18. For the inner cable 11, the tightening percentage is also 4 to 11% and the pre-forming percentage is 65 to 90%.
Further, another example of the inner cable described in Japanese Patent Publication No. 2669754 is shown in FIG. 3.
For the inner cable 21, the tightening percentage is also 4 to 11% and the pre-forming percentage is 65 to 90%, and it has a 7×7 construction. Namely, the core strand 22 is a strand in which 6 of the side element wires 24 is stranded around one core element wire 23. Further, the side strand 25 stranded around the core strand 22 is a strand in which 6 of the side element wires is stranded 27 around one core element wire 26, in the same manner as the core strand 22.
Since the tightening percentage is 4 to 11% and the pre-forming percentage is 65 to 90% for the inner cable described in Japanese Patent Publication No. 2669754, the durability of bending fatigue is not lowered even if it is used at a site sliding such as a guide device. Consequently, the inner cable described in Japanese Patent Publication No. 2669754 is used, for example, for a control cable for a window regulator of an automobile and the like.
However, when the inner cable described in Japanese Patent Publication No. 2669754 is used for the control cable for a window regulator of an automobile, there is a problem that abnormal noise is generated in accordance with the friction of the cable guide with the inner cable.
The present inventors have studied the cause of the abnormal noise and as a result, have found that the stranded trace of the inner cable is transcribed on the cable guide at a process of use, and stranded unevenness is formed. As a result, when the inner cable slides on the cable guide, rotational force works on the inner cable at sliding on the stranded unevenness to twist the inner cable and the twisting of the inner cable is released and hits the cable guide plane to generate abnormal noise.
It is described in “All of Wire Ropes (II)” edited by Steelmaking Activation Study Group of the Kaizuka Chamber of Commerce and Industry, published by the Kaizuka Chamber of Commerce and Industry, Jul. 25, 1995, pages 45 to 59 that the property of rotation centering on the axis of an inner cable means the rotation of the inner cable, the rotation of the inner cable includes rotation based on tension, rotation based on contact and rotation based on bending, and the rotation based on contact among these occurs by rotation caused by movement to a spiral direction when the inner cable is brought in contact with a sieve because grooves between strands are spiral on the surface of the inner cable because of stranding.
Further, relation between the stranded angle of an inner cable and a stranding length (inner cable pitch) is as shown in FIG. 4 and is represented by the following formula (1).tan α=dr·π/Pi   (1)
Wherein α is the stranded angle of an inner cable, Pi is a stranding length (pitch) and dr is a lay core diameter of an inner cable.
Further, according to “All of Wire Ropes (II)” edited by Steelmaking Activation Study Group of the Kaizuka Chamber of Commerce and Industry, published by the Kaizuka Chamber of Commerce and Industry, Jul. 25, 1995, pages 45 to 49, an inner cable in which the compensating relation of stranded return torque is improved in comparison with a rotating inner cable by elongating the stranding length of a strand in comparison with the inner cable of six rotating strands in the composition of six normal stranded strand inner cables is generally called as a long pitch inner cable or a hardly rotating inner cable.
The purpose of the invention of Japanese Unexamined Patent Publication No. 228277/1997 is to provide a hardly rotating complex lay stranded inner cable in which the de-stranding resistance of steel core at loading, the hooking force of an outer lay strand and the like are enhanced by composing with both inner lay strands with a normal stranded construction alternately disposing steel cores and the Lang lay construction, the rotation, shape loss and the like of the whole inner cable are effectively reduced, and steel cores can be used for both inner cables with a normal stranded construction and the Lang lay construction to improve the hardly rotating property, shape loss resistance, durability and the like and to reduce cost. In a complex lay stranded inner cable which is stranded by a plurality of outer lay strands on a steel core which is stranded by a plurality of inner strands, an inner strand formed to Z side and an inner strand formed to S side are alternately disposed to be stranded in the same direction to form steel cores equipped with the inner strand with a normal stranded construction and the inner strand with the Lang lay construction which are alternately disposed. A plurality of outer lay strands are stranded to the same direction in a normal stranded construction or the Lang lay construction such that the de-stranding resistance of steel core at loading, the hooking force of an outer lay strand and the like are enhanced by both inner lay strands with a normal stranded construction alternately disposed and the Lang lay construction, the rotation, shape loss and the like of the whole inner cable are effectively reduced together with the steel cores. Thereby steel cores can be used for both inner cable having a normal stranded construction and the Lang lay construction such that the hardly rotating property, shape loss resistance, durability and the like are improved and cost reduction can be carried out.
An object of the invention in Japanese Unexamined Patent Publication No. 295187/2001 is to remarkably reduce the damage of element wires in comparison with a conventional strand inner cable and to suppress the generation of sound between element wires caused by friction. In order to solve the problem, in a strand inner cable in which a plurality of element wires are stranded to form a core strand and a plurality of side strands which are formed by stranding a plurality of element wires around the core strand are stranded, element wires drawing spiral by stranding among element wires composing the core strand and element wires drawing spiral by stranding among element wires composing the side strands are entirely formed in the same length.
The invention described in Japanese Unexamined Patent Publication No. 295187/2001 found out that the difference in the length of element wires affects wear resistance and sound generated between respective element wires, and the concentration of stress applied to respective element wires is mitigated by equalizing the length of element wires. Therefore wear resistance is improved and the generation of sound generated between respective element wires is suppressed.